JP2007218901A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas gauge proximity sensor having a choked flow orifice for sensing a difference between a reference surface standoff and a measurement surface standoff. <P>SOLUTION: Unlike an existing proximity sensor, the gas gauge proximity sensor of the present invention replaces the use of a mass flow controller with the choked flow orifice. The use of the choked flow orifice provides a reduction in device cost and an improved system reliability. A gas supply forces gas into the proximity sensor. The gas flow is forced through the choked flow orifice so as to achieve a sonic condition at which a mass flow rate becomes largely independent of pressure variations. The flow of gas proceeds from the choked flow orifice into a sensor flow channel system. A mass flow sensor within the sensor flow channel system monitors the flow rate to detect the measurement standoffs that can be used to initiate a control action. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

[0001] The present invention is arranged to exhaust a gas through one or more openings including a gas supply source and a gas supply source and including at least one measurement opening. And a pressure sensor comprising a sensor channel system arranged to measure pressure in at least one measurement opening.

[0002] Many automated manufacturing processes require sensing of the distance between the manufacturing tool and the product or material surface being processed. In certain situations, such as semiconductor lithography, distances must be measured with an accuracy close to nanometers.

[0003] Problems related to the development of a proximity sensor having such an accuracy are important, particularly in the case of a photolithography system. In the case of photolithography, in addition to being non-intrusive and being able to accurately detect very short distances, proximity sensors must not introduce contaminants, usually Do not touch the work surface, which is a semiconductor wafer. If contaminants are introduced or contacted with the work surface, the quality of the semiconductor may be significantly degraded or completely ruined.

[0004] Several types of proximity sensors can be used to measure very short distances. Examples of proximity sensors include capacitance gauges and optical gauges. When used in a lithographic projection system, these proximity sensors have significant defects. This is because the physical properties of the material deposited on the wafer can affect the accuracy of these devices. For example, capacitance gauges that depend on the concentration of charge can exhibit false proximity measurements where one type of material (eg, metal) is concentrated. Other types of problems arise when using new types of wafers made of non-conductive and / or photosensitive materials such as gallium arsenide (GaAs) and indium phosphide (InP). In these cases, capacitance gauges and optical gauges can show incorrect measurements.

[0005] Andrew Barada's US Patent No. 4,953,388 (hereinafter the '388 patent), dated September 4, 1990, and titled "Air Gauge Sensor", and November 5, 1985 U.S. Pat. No. 4,550,592 (hereinafter the '592 patent) entitled “Pneumatic Gauging Circuit” by Michel Deschape discloses another approach for proximity sensing using an air gauge sensor. ing. The '388 and' 592 patents are hereby incorporated by reference in their entirety. These sensors emit a flow of air over the reference surface and the measurement surface to measure the distance between the measurement nozzle and the measurement surface, and a reference nozzle for measuring the difference in back pressure within the sensor and A sensor channel system with a measuring nozzle is used.

[0006] Furthermore, Burrows, VR, “The Principles and Applications of Air Measurement” published on pages 31-42 of the FWP Journal, published in October 1976, which is incorporated herein by reference in its entirety. Applications of Pneumatic Gauging) describes the principle of air measurement. Air gauge sensors are not affected by the charge on the wafer surface or the concentration of electrical, optical and other physical properties. However, in the case of current semiconductor manufacturing, proximity must be measured with a precision as high as nanometers. However, early air gauge sensors often do not meet current accuracy requirements in lithographic projection apparatus.

[0007] One improvement made to improve the accuracy of the air gauge sensor is to use a mass flow controller and a gas pressure regulator at the input to the mass flow controller to ensure that the flow from the gas supply is stabilized. That is. The mass flow controller dissipates heat and is mounted away from the sensor flow path system with a supply tube between the mass flow controller and the air gauge sensor. However, this supply tube has a volume. The larger the volume of the supply tube, the slower the response of the air gauge sensor. Because it dissipates heat, the mass flow controller is typically located in a cabinet that is remote from the wafer stage compartment of the lithographic projection apparatus. The wafer stage compartment is a compartment of a lithographic projection apparatus where the wafer is irradiated with a patterned beam of radiation while the wafer is supported on the wafer stage.

[0008] To make matters worse, the mass flow from the mass flow controller depends on the air pressure on the output side of the mass flow controller. The air pressure on the output side depends on the pressure at the measurement opening, which reduces the accuracy of the air gauge sensor. In order to overcome this drawback, an accumulator is installed on the output side of the mass flow controller in order to stabilize the pressure on the output side of the mass flow controller. However, this further increases the volume and slows the response of the air gauge sensor.

One object of the present invention is to provide a pressure sensor that can increase the possibility of arrangement.

[0010] The present invention provides a pressure sensor according to claim 1. In order to bring the flow state into choked flow, the gas source and restrictor are arranged so that the mass flow rate through the restrictor is controlled and the gas downstream from where the flow is choked flow. Unaffected by pressure fluctuations. This choked flow condition occurs at the restrictor. The gas supplied to the sensor channel system is controlled. This is because the restrictor is located upstream of the sensor flow path system. This means that a mass flow controller is no longer needed. An accumulator for stabilizing the pressure at the output of the mass flow controller is no longer necessary as well. Since the restrictor does not dissipate heat, the restrictor can be installed very freely. That is, this increases the possibility of placement of the pressure sensor.

[0011] Further embodiments, features and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.

[0012] The present invention will be described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.

[0017] While the present invention will be described below with reference to exemplary embodiments for specific applications, it should be understood that the present invention is not limited to these embodiments. Those skilled in the art will recognize upon reading this specification other modifications, applications and embodiments within the scope of the present invention, and other areas in which the present invention would be very useful.

[0018] Co-pending, commonly owned US patent application Ser. No. 10 / 322,768, entitled “High Resolution Gas Gauge Proximity Sensor” dated 19 December 2002, Gajdeczko et al. The '768 patent application) describes a high accuracy gas gauge proximity switch that overcomes some of the accuracy limitations of early air gauge proximity sensors. The accuracy limitation was overcome because a porous buffer was introduced to reduce turbulence in the gas flow and thereby improve accuracy. The '768 patent application, which is incorporated herein by reference in its entirety, describes a high accuracy gas gauge proximity sensor.

[0019] Joseph Lyons, dated August 25, 2003, co-pending and commonly owned US Patent Application No. 10 / 646,720 entitled "High Resolution Gas Gauge Proximity Sensor" '720 patent application) describes a proximity sensor that uses special nozzles to further improve accuracy and eliminate insensitive areas on the measurement surface during measurement operations. The entire text of the '720 patent application is incorporated herein by reference.

[0020] External acoustic interference may also affect the gas gauge proximity sensor. Co-pending, commonly owned US patent application Ser. No. 10 / 854,429 entitled “Gas Gauge Proximity Sensor with a Modulated Gas Flow” dated May 27, 2004 to Ebert et al. No. (hereinafter the '429 patent application) describes a gas gauge proximity sensor that modulates gas flow with a modulation frequency that includes minimal acoustic interference energy, thereby improving measurement accuracy. The entire text of the '429 patent application is hereby incorporated by reference.

[0021] Although the sensors disclosed in the '768,' 720, and '429 patent applications have high accuracy, this accuracy is affected by changes in local environmental conditions near the measurement and reference nozzles. There is a risk of receiving. In some environments, even if the nozzles are often very close to each other, the accuracy of the sensor can be affected by slight variations in environmental conditions. A co-pending, commonly owned US patent application Ser. No. 10 / 833,249 (hereinafter the '249 patent) entitled “High Resolution Gas Gauge Proximity Sensor” dated April 28, 2004 by Carter et al. Application) describes a gas gauge proximity sensor that includes a chamber that reduces the environmental differences between the measurement nozzle and the reference nozzle. The entire text of the '249 patent application is incorporated herein by reference.

[0022] A similar problem is associated with the cross flow of gas or liquid that intersects the flow of gas or liquid exiting the measurement flow path of the proximity sensor. More specifically, for example, the purge gas may contain a local cross wind at a speed on the order of a few meters per second. Crosswind or crossflow can cause the gauge to become unstable or staggered, causing errors in the proximity sensor that cannot be calibrated. Herman Vogel's co-pending, commonly owned US Patent Application No. 11/005, entitled “Proximity Sensor Nozzle Shroud with Flow Curtain,” dated 7 December 2004. No. 246 (hereinafter the '246 patent application) describes a proximity sensor that includes a shroud around the nozzle to reduce the effects on crosswind. The entire text of the '246 patent application is incorporated herein by reference.

[0023] The proximity sensor must be non-invasive. When the proximity sensor and the work surface come into contact with each other, there is a possibility that the quality of the semiconductor or the quality of the other work surface is significantly deteriorated or completely lost. However, in order to ensure the maximum level of accuracy, the measurement nozzle often has to be very close to the work surface. In some circumstances, a higher level of accuracy is required, so movement of the wafer stage or other work platform may be desirable to move the proximity sensor closer to or away from the work surface. As a result, another source of inaccuracy related to the mechanical stability of the proximity sensor head occurs when moving up and down. If the sensor head is extended, it will become unstable, which may reduce the accuracy of the proximity sensor. Co-pending, commonly owned US Patent Application No. 11/015, entitled “Proximity Sensor with Self Compensation for Mechanism Instability” dated December 20, 2004, by Peter Kochersperger No. 652 (hereinafter the '652 patent application) discloses a retractable proximity sensor that includes a self-compensating mechanism to reduce the effect of proximity sensor head misalignment on proximity sensor accuracy. The entire text of the '652 patent application is hereby incorporated by reference.

FIG. 1 is a view showing a gas gauge proximity sensor 100. The gas gauge proximity sensor 100 is one type of proximity sensor that can be improved by using the present invention and does not limit the scope of the present invention. The gas gauge proximity sensor 100 includes a gas pressure regulator 105, a mass flow controller 106, a central flow path 112, a measurement flow path 116, a reference flow path 118, a measurement flow path restrictor 120, a reference flow path restrictor 122, a measurement probe 128, a reference probe. 130, a bridge channel 136 and a mass flow sensor 138. The gas supply source 102 injects gas into the gas gauge proximity sensor 100 at a desired pressure.

The central flow path 112 connects the gas supply source 102 to the gas pressure regulator 105 and the mass flow controller 106 and extends to the branch portion 114. The gas pressure regulator 105 and the mass flow controller 106 maintain the flow rate in the gas gauge proximity sensor 100 constant.

The gas is pushed out from the mass flow controller 106 into the flow path 112 by the accumulator 108 attached to the flow path 112. The accumulator 108 is attached to the flow path 112 to stabilize the gas pressure at the output of the mass flow controller. This is because the output of the mass flow controller depends on the gas pressure at the outlet. In some situations, a buffer not shown in this figure can be installed between the mass flow controller 106 and the branch 114. The buffer reduces the turbulence of the gas introduced by the gas supply source 102. See the '249 patent application for details of the buffer 110. After leaving the mass flow controller 106, the gas is supplied to the branch 114 through the central flow path 112. The central channel 112 extends to the branching portion 114 and branches to the measurement channel 116 and the reference channel 118. The mass flow controller 106 injects gas at a sufficiently low rate to provide a laminar and incompressible fluid flow through the system in order to minimize the generation of undesirable aerodynamic noise. Similarly, the system geometry can be sized appropriately to maintain the laminar flow characteristics established by the mass flow controller 106.

[0027] Mass flow controllers, such as mass flow controller 106, are expensive and often cost thousands of dollars or more, especially when it is specified that they are less dependent on pressure fluctuations at the output. To do. The mass flow controller 106 dissipates heat and is mounted away from the other components of the gas gauge proximity sensor 100. A flexible supply tube couples the mass flow controller 106 to the branch 114. The supply tube is prone to leakage. Leaks are often small and usually do not affect other types of systems, but leaks can have a significant impact on the performance of gas gauge proximity sensors. Furthermore, the volume of the tube acts like a condenser. As the local pressure around the gas gauge proximity sensor changes, the flow through it changes and it takes several seconds for the flow to stabilize due to the capacitive function of the tube volume. This effect is even greater when an accumulator is added to stabilize the gas pressure at the output of the mass flow controller.

The bridge channel 136 connects the measurement channel 116 and the reference channel 118. The bridge channel 136 is connected to the measurement channel 116 at the branch portion 124. The bridge channel 136 is connected to the reference channel 118 at the branch portion 126. For example, the distance between the branch part 114 and the branch part 124 is equal to the distance between the branch part 114 and the branch part 126.

[0029] Gas can flow through all channels in the gas gauge proximity sensor 100. The channels 112, 116, 118, and 136 can include conduits (tubes, pipes, etc.) or any other type of structure that can guide the gas through the sensor 100. . Preferably, the flow path does not have sharp bends, irregularities or unnecessary obstructions that may cause aerodynamic noise, for example by creating local turbulence or unstable flow Is preferred. The total length of the measurement channel 116 and the reference channel 118 may be the same or may not be the same as in other examples.

The reference channel 118 extends to the reference nozzle 130. Similarly, the measurement channel 116 extends to the measurement nozzle 128. The reference nozzle 130 is located on the reference surface 134. The measurement nozzle 128 is located on the measurement surface 132. In the case of photolithography, the measurement surface 132 is often a semiconductor wafer, a stage that supports the wafer, a flat panel display, a printhead, a micro or nanofluidic device, or the like. The reference surface 134 may be a flat metal plate, but is not limited thereto. The gas injected by the gas supply source 102 is discharged from the nozzles 128 and 130 and enters the measurement surface 132 and the reference surface 134. As already explained, the distance between the nozzle and the corresponding measuring or reference surface is called a standoff.

[0031] The measurement flow path restrictor 120 and the reference flow path restrictor 122 serve to reduce turbulent flow in the flow path and operate as resistance elements. In other embodiments, other types of resistive elements such as orifices can be used. However, the orifice does not reduce turbulence.

The reference nozzle 130 is located on the fixed reference surface 134 with a known reference standoff 142 therebetween. The measurement nozzle 128 is located on the measurement surface 132 with an unknown measurement standoff 140. The known reference standoff 142 is set to a desired constant value that represents the optimum standoff. With this arrangement, the back pressure upstream of the measurement nozzle 128 is a function of the unknown measurement standoff 140, and the back pressure upstream of the reference nozzle 130 is a function of the known reference standoff 142. If the standoffs 140 and 142 are equal, the configuration is symmetric and the bridge is balanced. Therefore, no gas flows through the bridge channel 136. On the other hand, when the measurement standoff 140 and the reference standoff 142 are different, gas flows through the mass flow sensor 138 due to a pressure difference between the measurement flow path 116 and the reference flow path 118.

[0033] The mass flow sensor 138 is located along the bridge flow path 136, but is preferably located at the center of the flow path. The mass flow sensor 138 senses a gas flow due to a pressure difference between the measurement channel 116 and the reference channel 118. These pressure differences are due to changes in the vertical position of the measurement surface 132. In the case of a symmetric bridge, if the measurement standoff 140 and the reference standoff 142 are equal, the standoffs for both nozzles 128, 130 when compared to the surfaces 132, 134 are the same. The mass flow sensor 138 does not detect a mass flow. This is because there is no pressure difference between the measurement channel and the reference channel. If there is a difference between the measurement standoff 140 and the reference standoff 142, there will be a difference in the pressure in the measurement channel 116 and the reference channel 118. In the case of an asymmetrical arrangement, an appropriate offset can be introduced.

[0034] The mass flow sensor 138 senses a gas flow due to a pressure differential or pressure imbalance. The gas flows when the pressure difference is made, but the velocity is a unique function of the measurement standoff 140. That is, assuming that the flow rate into gas gauge 100 is constant, the difference in gas pressure in measurement channel 116 and reference channel 118 is a function of the difference between the magnitudes of standoffs 140 and 142. . When the reference standoff 142 is set to a known standoff, the difference in gas pressure in the measurement channel 116 and the reference channel 118 causes the measurement standoff 140 (i.e., the unknown stand between the measurement surface 132 and the measurement nozzle 128 to be unknown. Off) magnitude function.

The mass flow sensor 138 detects the gas flow in either direction through the bridge flow path 136. Due to the configuration of the bridge, the gas flows through the bridge channel 136 only when there is a pressure difference between the channels 116 and 118. If the pressure is unbalanced, the mass flow sensor 138 can detect the resulting gas flow and initiate an appropriate control function. The mass flow sensor 138 can display the flow sensed by a visual display, an acoustic display, a computer control system or other signal means. Alternatively, a differential pressure sensor can be used instead of the mass flow sensor. The differential pressure sensor measures the pressure difference between the two channels that is a function of the difference between the measurement standoff and the reference standoff.

[0036] The proximity sensor 100 is an example of a device having a nozzle according to the present invention. The present invention is not limited to use with proximity sensor 100. On the contrary, the present invention relates to other types of proximity sensors such as those disclosed in the '388 and' 592 patents and the '768,' 720, '429,' 249, '286 and' 652 patent applications, for example. Can be used to improve.

FIG. 2 is a drawing of a proximity sensor 200 according to one embodiment of the present invention. The difference between proximity sensor 200 and proximity sensor 100 is that, instead of mass flow controller 106, receives gas from gas source 202 and is located upstream of a sensor flow system described in more detail below, choked flow orifice 207. Is to use. The gas supply source 202 includes a gas pressure regulator 205 that supplies gas at a controlled pressure in the choked flow orifice 207. The sensor channel system includes a measurement channel 216, a reference channel 218, a measurement channel restrictor 220, a reference channel restrictor 222, a measurement probe 228, a reference probe 230, a bridge channel 236, A mass flow sensor 238. The measurement channel 216 and the reference channel 218 are coupled at the branching portion 214.

The central channel 212 connects the gas supply source 202 to the gas pressure regulator 205 and the choked flow orifice 207 and then extends to the branch 214. The gas pressure regulator 205 and the choked flow orifice 207 maintain the mass flow rate in the gas gauge proximity sensor 200 constant, as will be described below. The gas is pushed out from the choked flow orifice 207 into the channel 212. In some situations, a buffer not shown in this figure can be placed between the choked flow orifice 207 and the bifurcation 214. After exiting the choked flow orifice 207, the gas flows through the central flow path 212 to the branch 214.

[0039] When the gas passing through the choked flow orifice becomes a sonic velocity, a choked flow state is created in the gas. Some of the gas flow through the choked flow orifice 3, the sound velocity condition occurs when downstream the ratio of the pressure P ₂ of the relative pressure P ₁ on the upstream is about 0.528 or less. When in the sonic state, the velocity of the gas exiting the choked flow orifice 207 is constant for all pressure ratios below about 0.528. As a result, the use of the choked flow orifice 207 eliminates the effect of a small pressure drop that occurs in the case of a small amount of leakage and provides a constant gas flow through the pressure sensor flow path structure.

[0040] As already explained, the velocity in the orifice is not affected by pressure fluctuations in choked flow conditions. Further, in the case of choked flow, the mass flow rate through the choked flow orifice 207 is not affected by the pressure difference downstream of the choked flow orifice. Therefore, the mass flow rate is also unaffected by pressure fluctuations at both the measurement probe 228 and the reference probe 230, so-called common mode pressure fluctuations. The choked flow condition is established by estimating the worst common mode pressure variation, supplying gas to the choked flow orifice at a sufficiently high pressure. The worst case common mode pressure variation corresponds to the maximum expected gas pressure just downstream of the restrictor. This determines the threshold pressure of the gas supplied to the choked flow orifice. As described below, in one embodiment of the present invention, a gas pressure regulator is used to supply gas to the choked flow orifice. In the preferred embodiment, the regulated pressure is a constant pressure above the threshold.

[0041] When the proximity sensor 200 is installed in a lithographic apparatus to detect the proximity of a wafer, common mode pressure fluctuations may occur frequently. For example, such fluctuations may be caused by changes in the pressure of a clean room in which the lithographic apparatus is installed. Such a change in pressure may occur because the pressure in such a clean room is maintained higher than the ambient pressure. The reason why the pressure is maintained is to prevent dust from entering the clean room. The pressure drops every time the operator opens the door to enter the clean room. The lithographic apparatus also includes a member that moves at high speed, such as a wafer table. A wafer table is a device that supports a wafer when measuring the wafer and when irradiating the wafer. When these wafer tables move at a high speed, a leading wave is generated, and the leading wave corresponds to a change in pressure.

[0042] It is undesirable to be sensitive to common mode pressure fluctuations. This is because if it is sensitive, the accuracy of the measurement will be low. The accuracy of the proximity sensor measurement depends on the stability of the mass flow rate through the reference channel 218. This is because the mass flow sensor 238 is calibrated to display the pressure difference as a function of the mass flow rate through the mass flow sensor 238 for a constant mass flow rate through the reference channel 218. A mass flow sensor if mass is flowing through the bridge channel 236 and both through the measurement channel 216 and the reference channel 218 that change due to common mode pressure fluctuations (with equal pressure differences). 238 detects a change in mass flow rate through the bridge channel 236. The sensor then causes mass flow changes through the bridge channel 236 to be greater between the measurement probe 238 and the reference probe 230 at a constant air flow through both the measurement channel 216 and the reference channel 218. It is misinterpreted as being due to a pressure difference. Therefore, the accuracy of the measured value of this sensor is lowered. The mass flow rate through the bridge channel varies. This is because the pressure profile from the branch 226 to the reference nozzle 230 is not linear, and the pressure profile from the branch 224 to the measurement nozzle 228 is not linear.

[0043] Although the mass flow controller 106 of the pressure sensor 100 dissipates heat, the choked flow orifice comprising the pressure sensor of the present invention does not dissipate heat, so it is necessary to install this orifice at a position away from the branching portion 214. Absent. An advantageous use of this orifice will be described later.

[0044] In a lithographic apparatus, a wafer is exposed to a radiation beam at an exposure station. Before that, several faces of the wafer are measured at the measuring station. Such surfaces are the position of the wafer relative to the wafer stage supporting the wafer, the position of the alignment mark on the wafer, and the thickness of the wafer. In current lithographic apparatuses, the exposure station and the measuring station are separate, but in previous lithographic apparatuses these stations were integrated.

[0045] In one embodiment, the wafer (or other substrate) is supported by a substrate stage. The position of the substrate stage is continuously measured and controlled, and is changed by positioning means when necessary. The substrate stage includes a table that actually supports one side of the substrate. Pressure sensor (Gas Gauge Proximity Sensor) measures to measure the proximity of the wafer to the pressure sensor while tracking the wafer position and scanning the wafer under the gas gauge proximity sensor, as already explained Can be used at the station. A map of the wafer thickness is created by comparing the position of the wafer stage, thereby comparing the wafer with the proximity of the wafer to the gas gauge proximity sensor at multiple positions along the scan. As a result, predetermined information about the position of the pressure sensor relative to the substrate stage is used.

[0046] However, since the lithographic apparatus comprises many devices that are very accurate but sensitive to changes in temperature, very high reference temperature control is applied. For this reason, a device that dissipates an amount of heat that exceeds a threshold cannot be used in the measurement station.

[0047] The mass flow controller 106 of the proximity sensor of the prior art is a device that cannot be used at the measurement station. Therefore, the mass flow controller is installed at a location remote from the measurement station, such as in a special temperature control cabinet. Since the heat dissipation in the temperature control cabinet is controlled separately, it does not affect the performance of the rest of the machine. A long central channel 112 is used to guide the gas from the mass flow controller 106 to the measurement channel 116 and the reference channel 118. Its length can be several meters.

[0048] The choked flow orifice 207 comprising the pressure sensor of the present invention does not dissipate as much heat as the mass flow controller 106, so that the orifice can be used as a measurement opening 228 and a reference opening 230 (or branch 214 or measurement). It is not necessary to install it far away from the channel 216 and the reference channel 218).

[0049] Since the choked flow orifice 207 can be freely installed, the space between the choked flow orifice and the measurement probe 228 and the reference probe 230 is selected to be as small as possible. This is because the wider the space, the slower the frequency response of the proximity sensor 200. The space between the choked flow orifice 207 and the restrictors 220 and 222 is part of the space between the choked flow orifice and the measurement probe 228 and the reference probe 230. In some embodiments, the choked flow orifice, the restrictor 207, is located near or at the inlet of the sensor flow system (the branch 214 and a portion of the downstream pressure sensor). For the lithographic apparatus, being located near or at the entrance means that the restrictor 207 is located in the substrate stage compartment. That is, it is located in a compartment of a lithographic apparatus that is arranged to include at least one substrate stage for supporting the substrate while irradiating the substrate with a beam including a patterned cross section. The substrate stage compartment is an area in the lithographic apparatus that is typically located under a very near temperature controller. This is because the compartment typically includes an interferometer that tracks the position of the substrate stage. Interferometers are sensitive to temperature changes.

[0050] When the choked flow orifice is installed near or at the inlet, the space of the central flow path 212 is much smaller, that is, several steps smaller than the space of the central flow path 112 of the pressure sensor 100. Therefore, the pressure sensor 200 responds to local pressure changes much faster than the proximity sensor 100. On the top surface, the accumulator as described for the proximity sensor 100 is not used in the pressure sensor 200. Such an accumulator has a higher frequency response than the proximity sensor 100 because it increases volume and thereby slows the response of high frequencies.

Between the gas supply source 202 and the choked flow orifice 207, a gas pressure regulator 205 having an output (not shown) for supplying gas pressurized gas to the choked flow orifice 207 is located. The gas pressure regulator 205 supplies gas at a constant pressure at its output (not shown) regardless of the gas pressure of the gas supplied from the gas supply source 202 to the gas pressure regulator 205. This means that even when there is a leak between the gas supply source 202 and the gas pressure regulator 205, the gas pressure regulator 205 supplies gas at a constant pressure. The choked flow orifice 207 has an input (not shown) that receives the gas supplied by the gas pressure regulator 205. The output of gas pressure regulator 205 is coupled to the input of choked flow orifice 207. Although the mass flow rate controlled by the choked flow state depends on the pressure fluctuation upstream of the choked flow state, the pressure sensor of this embodiment does not depend on the pressure fluctuation. This is because the pressure fluctuation upstream of the choked flow state is controlled by the gas pressure regulator 205.

[0052] For example, in other embodiments where the pressure of the gas supplied by the gas source 202 is sufficiently stable for the intended use of the pressure sensor, the gas is passed through a pressure sensor having a gas pressure regulator. Not supplied to the choked flow orifice.

[0053] In one embodiment, the pressure sensor 200 comprises a temperature controller (not shown) arranged to control the temperature of the gas supplied to the restrictor (207). Thereby, the mass flow rate downstream of the choked flow orifice 207 is further stabilized. This is because the mass flow rate through the choked flow orifice 207 depends slightly on the temperature of the gas upstream of the choked flow orifice.

[0054] A choked flow orifice, such as the choked flow orifice 207, may be obtained from a company that manufactures specialized controllers. For example, O'Keefe Control, Inc., located in Trumbull, Connecticut, sells sapphire orifices with an integral wire screen that can be used.

[0055] The architecture of the proximity sensor 200 after the choked flow orifice 207 is the same as the architecture of the proximity sensor 100. Of course, there is a difference that the central channel 212 has a much smaller space than the central channel 112. Part of the architecture after the choked flow orifice 207 can be considered a sensing flow path system. The sensing channel system described below is an example of a sensing channel system that can be used with a gas source and a choked flow orifice to form a proximity sensor. For example, other sensing channel systems such as those disclosed in the '388 and' 592 patents and the '768,' 720, '429,' 249, '246 and' 652 patent applications are also used. Can do. Other architectures of the proximity sensor 200 are also described for completeness.

The central flow path 212 extends to the branch portion 214 and branches to the measurement flow path 216 and the reference flow path 218. The choked flow orifice 207 injects gas at a sufficiently low rate to provide a laminar and incompressible fluid flow throughout the system for the purpose of minimizing the generation of undesirable aerodynamic noise. Similarly, the system geometry can be sized appropriately to maintain the laminar flow characteristics established by the choked flow orifice 207.

The bridge channel 236 couples between the measurement channel 216 and the reference channel 218. The bridge channel 236 is connected to the measurement channel 216 at the branch 224. The bridge channel 236 is connected to the reference channel 218 at the branch 226. For example, the distance between the branch part 214 and the branch part 224 is equal to the distance between the branch part 214 and the branch part 226. Channels 216 and 218 include channel restrictors 220 and 222, respectively. These restrictors will be described in detail below.

[0058] Gas may flow through all channels in the gas gauge proximity sensor 200. The flow paths 212, 216, 218 and 236 can include conduits (tubes, pipes, etc.) or any other type of structure that can guide the gas through the sensor 200. . Preferably, the flow path does not have sharp bends, irregularities or unnecessary obstructions that may cause aerodynamic noise, for example by creating local turbulence or unstable flow Is desirable. The overall length of the measurement channel 216 and the reference channel 218 may be the same, or may not be the same as in other examples.

The reference channel 218 extends to the reference nozzle 230. Similarly, the measurement channel 216 extends to the measurement nozzle 228. The reference nozzle 230 is located on the reference surface 234. The measurement nozzle 228 is located on the measurement surface 232. In the case of photolithography, the measurement surface 232 is often a semiconductor wafer, a stage supporting the wafer, a flat panel display, a printhead, a micro or nanofluidic device, or the like. The reference surface 234 may be a flat metal plate, but is not limited thereto. The gas injected by the gas supply source 202 is discharged from the nozzles 228 and 230 and is incident on the measurement surface 232 and the reference surface 234. As already explained, the distance between the nozzle and the corresponding measuring or reference surface is called the standoff.

[0060] The measurement flow path restrictor 220 and the reference flow path restrictor 222 serve to reduce turbulent flow in the flow path and operate as resistance elements. In other embodiments, other types of resistive elements such as orifices can be used. However, the orifice does not reduce turbulence.

[0061] In one embodiment, the reference nozzle 230 is located on the fixed reference surface 234 with a known reference standoff 242 therebetween. Measurement nozzle 228 is positioned on measurement surface 232 across an unknown measurement standoff 240. The known reference standoff 242 is set to a desired constant value that represents the optimum standoff. With this arrangement, the back pressure upstream of the measurement nozzle 228 is a function of the unknown measurement standoff 240, and the back pressure upstream of the reference nozzle 230 is a function of the known reference standoff 242. If the standoffs 240 and 242 are equal, the configuration is symmetric and the bridge is balanced. Therefore, no gas flows through the bridge channel 236. On the other hand, if the measurement standoff 240 and the reference standoff 242 are different, gas flows through the mass flow sensor 238 due to the resulting pressure difference between the measurement channel 216 and the reference channel 218.

[0062] The mass flow sensor 238 is located along the bridge channel 236, but is preferably located in the center of the channel. The mass flow sensor 238 senses a gas flow due to a pressure difference between the measurement channel 216 and the reference channel 218. These pressure differences are due to changes in the vertical position of the measurement surface 232. In the case of a symmetric bridge, if the measurement standoff 240 and the reference standoff 242 are equal, the standoffs for both nozzles 228, 230 when compared to the surfaces 232, 234 are the same. The mass flow sensor 238 does not detect mass flow. This is because there is no pressure difference between the measurement channel and the reference channel. If there is a difference between the measurement standoff 240 and the reference standoff 242, there will be a difference in the pressure in the measurement channel 216 and the reference channel 218. In the case of an asymmetrical arrangement, an appropriate offset can be introduced.

[0063] Mass flow sensor 238 senses gas flow due to pressure differential or pressure imbalance. The gas flows when the pressure difference is made, but the velocity is a unique function of the measurement standoff 240. That is, assuming that the flow velocity into gas gauge 200 is constant, the difference in gas pressure in measurement channel 216 and reference channel 218 is a function of the difference between the magnitudes of standoffs 240 and 242. . When the reference standoff 242 is set to a known standoff, the difference in gas pressure between the measurement channel 216 and the reference channel 218 causes the measurement standoff 240 (ie, the unknown standoff between the measurement surface 232 and the measurement nozzle 228). ) Is a function of length.

[0064] The mass flow sensor 238 detects the flow of gas in either direction through the bridge channel 236. Due to the bridge configuration, the gas flows through the bridge channel 236 only when there is a pressure difference between the channels 216, 218. If the pressure is unbalanced, the mass flow sensor 238 can detect the resulting gas flow and initiate an appropriate control function. The mass flow sensor 238 can display the flow sensed by visual display or acoustic display. Alternatively, a differential pressure sensor can be used instead of the mass flow sensor. The differential pressure sensor measures the pressure difference between the two channels that is a function of the difference between the measurement standoff and the reference standoff.

[0065] The proximity sensor 200 is an example of a device having a nozzle according to the present invention. The present invention is not limited to use with proximity sensor 200. On the contrary, to improve other types of proximity sensors such as, for example, the proximity sensors disclosed in the '388 and' 592 patents and the '768,' 720, '429,' 249, '286 and' 652 patent applications. In addition, a choked flow orifice can be used in place of the mass flow controller.

[0066] FIG. 4 is a flowchart of a method 400 for using a gas flow to detect very short distances and perform control actions. For convenience, the method 400 will be described with reference to the gas gauge proximity sensor 200. However, the method 400 is not necessarily limited by the structure of the sensor 200 and can be implemented with sensors of different structures.

[0067] The process starts at step 410. In step 410, the operator or machine places the reference probe above the reference plane. For example, an operator or mechanical device places the reference probe 230 above the reference surface 234 across a known reference standoff 214. Alternatively, the reference standoff can be placed in the sensor assembly, i.e. within the sensor assembly. The reference standoff is pre-adjusted to a specific value that is usually kept constant.

[0068] In step 420, the operator or mechanical device places the measurement probe above the measurement surface. For example, an operator or mechanical device positions measurement probe 228 over measurement surface 232 to form measurement gap 240.

[0069] In step 430, gas is injected into the sensor. For example, the measurement gas is injected into the gas gauge proximity sensor 200 at a constant mass flow rate.

[0070] In step 440, gas is forced through the choked flow orifice. For example, gas can be forced through the choked flow orifice 207 to achieve a sonic state, at which point the mass flow through the choked flow orifice is less dependent on the pressure differential. A constant gas flow rate into the sensor is maintained. For example, the choked flow orifice 207 maintains a constant gas flow rate.

[0071] In step 450, the gas flow is distributed between the measurement channel and the reference channel. For example, the gas gauge proximity sensor 200 distributes the flow of the measurement gas evenly between the measurement channel 216 and the reference channel 218.

[0072] In step 460, the gas flow in the measurement channel and the reference channel is evenly restricted across the cross section of the channel. Measurement channel restrictor 220 and reference channel restrictor 222 reduce aerodynamic noise and restrict gas flow to function as a resistive element within gas gauge proximity sensor 200.

[0073] In step 470, gas is forced out of the reference and measurement probes. For example, the gas gauge proximity sensor 200 forcibly discharges gas from the measurement probe 228 and the reference probe 230. In step 480, gas flow is monitored through a bridge channel connecting the reference channel and the measurement channel. In step 490, a control operation is performed based on the pressure difference between the reference channel and the measurement channel. For example, the mass flow sensor 238 monitors the mass flow rate between the measurement channel 216 and the reference channel 218. Based on the mass flow rate, the mass flow sensor 238 starts a control operation. Such a control action may include the step of displaying a sensed mass flow rate, sending a message indicating the sensed mass flow rate, or measuring plane relative to the reference plane until no fixed mass flow or mass flow reference value is sensed. The step of starting a servo control operation for changing the position of the control unit may be included. In step 495, the method 400 ends.

[0074] While various embodiments of the present invention have been described above, it should be understood that these embodiments are merely illustrative and do not limit the invention. Those skilled in the art will recognize that various changes in form and detail can be made without departing from the spirit and scope of the invention. As already described, the pressure sensor may or may not include the gas pressure regulator 205. The pressure sensor can also comprise one or several measurement channels. Arranged to receive gas from the restrictor (207) and guide the gas from the restrictor to one or more bridge branches (224) of one or more conduits having a bridge (236); One or more conduits (216) with one or more other limiting elements (220) upstream of the one or more bridge branches may be used. Additionally or alternatively, the pressure sensor can include several reference channels, such as reference channel 218. Further, the reference channel may not be used. The present invention is not limited to the use of air, for example. Instead, the invention also applies to gas pressure sensors.

[0075] The invention has been described in terms of method steps that indicate the performance of a specified function and its relationship. In the present specification, for the sake of explanation, the boundaries of these method steps are only defined in an ambiguous manner. Other boundaries can be defined as long as the specified function and its relationships are correct. Therefore, any such other boundaries are within the scope and spirit of the present invention. Accordingly, the scope of the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents.

[0076] The detailed description is primarily to be used to interpret the claims. The summary and summary describe one or more but not all exemplary embodiments of the invention as contemplated by the inventors and are not intended to limit the scope of the claims.

[0013] FIG. 3 is a diagram illustrating a proximity sensor. [0014] FIG. 5 illustrates a gas proximity sensor having a choked flow orifice according to one embodiment of the invention. [0015] Fig. 5 is a view showing a choked flow orifice. [0016] FIG. 6 is a flowchart of a method for detecting very short distances using a gas gauge proximity sensor having a choked flow orifice according to an embodiment of the invention.

Claims (16)

A gas supply source (202);
Arranged to be supplied with gas by said gas supply, arranged to discharge gas through one or more openings (228, 230) including at least one measurement opening (228); and A sensor flow path system (212, 214, 216, 218, 236) arranged to measure pressure at said at least one measurement opening,
A restrictor (207) located upstream of the sensor flow path system and arranged to receive gas from the gas supply source (202);
The gas supply source (202) and the restrictor (207) are arranged to obtain a choked flow state of the gas flowing into the sensor flow path system;
A pressure sensor characterized by that. The restrictor (207) comprises a choked flow orifice;
It is characterized by
The pressure sensor according to claim 1. The restrictor (207) is located near the inlet of the sensor flow path system;
The inlet is arranged to receive gas from the gas supply;
The pressure sensor according to claim 1 or 2, wherein The restrictor (207) is located at the inlet of the sensor flow path system;
The pressure sensor according to claim 3. The gas source (202) and the restrictor (207) are at least equal to a gas pressure immediately upstream of the restrictor and a threshold corresponding to a maximum expected gas pressure immediately downstream of the restrictor; Arranged to maintain a ratio between the gas pressure just downstream of the restrictor,
The pressure sensor according to any one of the preceding claims. The gas source comprises a pressure regulator (205) arranged to supply gas to the restrictor at a regulated pressure;
The pressure sensor according to any one of the preceding claims. The one or more openings comprise at least one reference opening (230);
The sensor flow path system is arranged to measure a pressure difference between the at least one measurement opening (228) and the at least one reference opening (230);
The pressure sensor according to any one of the preceding claims. The sensor channel system is
A measurement branch (216, 220, 228) comprising said at least one measurement opening (228);
A reference branch (218, 222, 230) comprising the at least one reference opening (230);
Measuring a pressure difference between the at least one measurement opening and the at least one reference opening between the measurement branch and the reference branch and upstream of the measurement opening and the reference opening. The arranged bridges (236, 238);
The pressure sensor according to claim 7, further comprising: The gas supplied through the restrictor (207) to the measurement branch (216, 222, 228) and the reference branch (218, 220, 230) is located upstream of the bridge (236, 238). Comprising a bifurcation (214) arranged to be sent,
The pressure sensor according to claim 8. Comprising one or more conduits (216, 218) for receiving gas from the restrictor (207);
The one or more conduits pass gas from the restrictor to one or more bridge branches (224, 226) of the bridge (236, 238) of the one or more conduits (216, 218). And one or more other limiting elements (220, 222) upstream of the one or more bridge branches,
The pressure sensor according to claim 8 or 9, wherein The one or more other limiting elements comprise a porous buffer;
The pressure sensor according to claim 10. Comprising a temperature controller arranged to control the temperature of the gas received by the restrictor (207);
The pressure sensor according to any one of the preceding claims. Comprising a pressure sensor according to any one of the preceding claims and an exposure station for exposing the substrate to a radiation beam having a pattern in cross-section.
Lithographic apparatus. A measurement station for measuring one or more surfaces of the substrate before exposing the substrate;
The sensor flow path system and the restrictor are disposed at the measurement station of the lithographic apparatus;
A lithographic apparatus according to claim 13, wherein the apparatus is a lithographic apparatus. The lithographic apparatus is arranged to provide a relative position to the at least one measurement opening (228) and the substrate, whereby gas exhausted from the at least one measurement opening strikes the substrate;
15. A lithographic apparatus according to claim 14, wherein: The restrictor (207) and the sensor flow path system are arranged to have at least one substrate stage for supporting the substrate while irradiating the substrate with a beam having a patterned cross section. Located in the substrate stage compartment of the lithographic apparatus,
A lithographic apparatus according to any one of claims 13 to 15, characterized in that